DESCRIPTION: (Applicant's Abstract) This is a proposal, in response to RFA HD-OO-0004, to perform a histological screen for ENU-induced mutations causing either organ-specific or general histological phenotypes in 7 day old parthenogenetic haif-tetrad larvae of zebrafish (Danio rerio). Subgoals include confinnation of each mutation as an inheritable trait, preliminary characterization, and mapping of each mutation to a chromosome arm. Community functions will include posting of mutant phenotypes on the web, and distribution of mutants to the Zebrafish Stock Center. We expect to find mutants with defective tissue differentiation, and to produce models for aspects of human disease, including cancer and diseases of the eye and gastrointestinal tract. The motivation for the screen is the power of histologic analysis in the characterization of pathological changes in human tissues. Hundreds of cell types and pathological changes are distinguishable from the light microscopic study of stained tissue sections. For example, the histological changes common to all cancers include defects in tissue organization and in the cytological appearance of cancer cells. A genetic dissection of these changes can be accomplished through the generation and study of mutants with histological phenotypes. The experimental features of the zebrafish make it an ideal vertebrate model to identify mutants with histological phenotypes. Each female can produce hundreds of embryos per week at a relatively low cost. Recessive mutations carried by females may be unmasked in parthenogenetic half-tetrad progeny. A pilot histologic screen 01 half-tetrad families of 72 carrier females produced two mutations affecting the neural retina, two affecting the gastrointestinal tract, and two with multi-organ effects (Cheng et al.,submitted). One mutant showed a strong cytological phenotype in multiple organs that would be diagnostic of severe atypia or cancer in a human cytology specimen. The screen's success establishes the ability of this laboratory to perform all required steps in the proposed screen, including mutagenesis, parthenogenesis, histologic screening, and mapping. This project will contribute to an elucidation of both organ-specific and general pathways of cell differentiation in vertebrates.